1. Field of the Invention
This invention relates to a surface-mounted type electronic component having a mounting surface to be mounted on a printed circuit board or a hybrid IC (HIC).
2. Description of the Related Art
Coil components mounted on internal circuitry of electronic equipment such as personal computers and cell phones include those of the winding type having two copper wires wound on a ferrite core, those of the laminated type obtained by forming a coil conductor pattern on the surface of a magnetic sheet such as of ferrite and laminating the magnetic sheets, and those of the thin film type obtained by alternately forming an insulating film and a coil conductor of a thin metal film relying on a thin film-forming technology.
JP-A-8-203737 discloses a common-mode choke coil that is used as a thin film type coil component. FIGS. 7A to 7C illustrate a state where a common mode choke coil array 101 formed by integrating two common mode choke coils is mounted on a printed circuit board (PCB) 121. 7A is a perspective view illustrating the appearance of the common mode choke coil array 101, FIG. 7B is a view illustrating, on an enlarged scale, an external electrode 114 connected to an internal electrode terminal 125 exposed to the side surface of the common mode choke coil array 101, and FIG. 7C is a view illustrating, on an enlarged scale, a state where an external electrode 114 shown in FIG. 7B is formed having a small width.
Referring to FIG. 7A, the common mode choke coil array 101 has a structure in which an insulating layer 107, a coil layer that is not shown, a magnetic layer 109 and an adhesive layer 111 are successively formed by the thin film-forming technology between the magnetic substrates 103 and 105 that are arranged facing each other. The internal electrode terminals 123, 125, 127 and 129 exposed to the insulating layer 107 are connected to the external electrodes 113, 114, 117 and 118. The internal electrode terminals (not shown) formed on the side surface facing the side surface on which the external electrodes 113, etc. are formed, are connected to the external electrodes 115, 116, 119 and 120, respectively.
Referring to FIGS. 7A and 7B, the external electrode 114 has rectangular electrode pads 114b and 114c formed, in an opposing manner, on the peripheral ends on the mounting surfaces of the magnetic substrates 103 and 105, and a connection electrode 114a formed on the outer surface on where the internal electrode terminal 125 is exposed. The connection electrode 114a electrically connects the internal electrode terminal 125 to the electrode pads 114b and 114c. 
The external electrodes 113, 117 and 118, too, have rectangular mounting pads 113b, 117b and 118b formed on the peripheral ends on the mounting surface of the magnetic substrate 105, rectangular electrode pads (not shown) formed on the peripheral ends on the mounting surface of the magnetic substrate 103 being opposed to the mounting pads 113b, 117b and 118b, and connection electrodes 113a, 117a and 118a formed on the outer surface on where the internal electrode terminals 123, 127 and 129 are exposed. The connection electrodes 113a, 117a and 118a are electrically connecting together the internal electrode terminals 123, 127 and 129, the electrode pads 113b, 117b and 118b, and the electrode pads formed on the mounting surface of the magnetic substrate 103.
Similarly, further, the external electrodes 115, 116, 119 and 120 have electrode pads 115b, 116b, 119b and 120b formed on the mounting surface of the magnetic substrate 105 on the side of the opposing outer surface, electrode pads (not shown) formed on the mounting surface of the magnetic substrate 103, and connection electrodes (not shown) formed on the opposing outer surface.
Here, the trend toward fabricating electronic equipment such as personal computers and cell phones in ever small sizes is requiring a decrease in the size and thickness (height) of electronic component s or chips such as coils. The coils of the winding type are accompanied by a problem of difficulty in decreasing the size due to the limitation on the structure. On the other hand, the coils of the laminated type and the common mode choke coil array 101 of the thin film type can be fabricated in small sizes having decreased heights owing to their structures.
To decrease the size of the common mode choke coil array 101, it is necessary to shorten the length L of the coil array 101 shown in FIG. 7A. To shorten the length L, the widths of regions forming the external electrodes 113 to 120 (gap a among electrodes +width c of electrodes) may be shortened. It can, therefore, be contrived to shorten the gap a among the neighboring external electrodes 113 to 120 without varying the width c of the external electrodes 113 to 120. Here, though the magnetic substrates 103 and 105 have a sufficiently high resistivity, the magnetic layer 109 have a relatively low resistivity. Therefore, the resistivity among the neighboring external electrodes 113 to 120 decreases with a decrease in the gap a among the neighboring external electrodes 113 to 120. If the gap a is very shortened, therefore, it is probable that a current flows among the neighboring electrodes via the magnetic layer 109, lowering the electrical reliability of the common mode choke coil array 101. Therefore, shortening the length L imposes limitation on decreasing the gap a among the external electrodes 113 to 120.
Referring, next, to FIG. 7C, therefore, it can be contrived to shorten the width of the external electrodes 113 to 120 from c to c′ (c′<c) while suppressing the gap a among the electrodes to be a required minimum value. First, by giving attention to the electrode pads 114b and 114c, the electrode pads 114b and 114c are formed by the electrode material that turns onto the mounting surfaces at the time of forming the connection electrode 114a. Therefore, a maximum pad width b of the electrode pads 114b and 114c becomes nearly equal to the width of the connection electrode 114a. If the electrode width of the connection electrode 114a is set to be c′, therefore, the pad width b of the electrode pads 114b and 114c is shortened. Accordingly, the area decreases on where the electrode pad 114c comes into contact with a solder land pattern 122 on the PCB 121. The coil array 101 is electrically and mechanically connected to the PCB 121 by a solder 133 formed on the solder land pattern 122. If the contact area of the electrode pad 114c to the solder land pattern 122 decreases, therefore, the mounting strength of the coil array 101 decreases. The same also holds for the electrode pads 113b and 113c other than the electrode pad 114c. Thus, the reliability for mounting the coil array 101 decreases with a decrease in the width of electrodes such as the connection electrodes 114a, etc. In shortening the length L, therefore, limitation is imposed on decreasing the electrode width c of the external electrodes 113 to 120.